Crystallization processing of semiconductor film regions on a substrate, and devices made therewith

ABSTRACT

Semiconductor integrated devices such as transistors are formed in a film of semiconductor material formed on a substrate. For improved device characteristics, the semiconductor material has regular, quasi-regular or single-crystal structure. Such a structure is made by a technique involving localized irradiation of the film with one or several pulses of a beam of laser radiation, locally to melt the film through its entire thickness. The molten material then solidifies laterally from a seed area of the film. The semiconductor devices can be included as pixel controllers and drivers in liquid-crystal display devices, and in image sensors, static random-access memories (SRAM), silicon-on-insulator (SOI) devices, and three-dimensional integrated circuit devices.

This Application is a continuation of PCT/US96/07730 filed Mar. 28,1996.

TECHNICAL FIELD

The invention relates to semiconductor materials processing forsemiconductor integrated devices.

BACKGROUND OF THE INVENTION

Semiconductor devices can be made in a layer or film of silicon on aquartz or glass substrate, for example. This technology is in use in themanufacture of image sensors and active-matrix liquid-crystal display(AMLCD) devices. In the latter, in a regular array of thin-filmtransistors (TFT) on an appropriate transparent substrate, eachtransistor serves as a pixel controller. In commercially available AMLCDdevices, the thin-film transistors are formed in hydrogenated amorphoussilicon films (a-Si:H TFTs).

In the interest of enhanced switching characteristics of TFTs,polycrystalline silicon has been used instead of amorphous silicon. Apolycrystalline structure can be obtained by excimer-lasercrystallization (ELC) of a deposited amorphous or microcrystallinesilicon film, for example.

However, with randomly crystallized poly-silicon, the results remainunsatisfactory. For small-grained poly-silicon, device performance ishampered by the large number of high-angle grain boundaries, e.g., inthe active-channel region of a TFT. Large-grained poly-silicon issuperior in this respect, but significant grain-structure irregularitiesin one TFT as compared with another then result in non-uniformity ofdevice characteristics in a TFT array.

SUMMARY OF THE INVENTION

For improved device characteristics and device uniformity, a lateralsolidification technique is applied to a semiconductor film on asubstrate. The technique, which may be termed artificially controlledsuper-lateral growth (ACSLG), involves irradiating a portion of the filmwith a suitable radiation pulse, e.g. a laser beam pulse, locally tomelt the film completely through its entire thickness. When the moltensemiconductor material solidifies, a crystalline structure grows from apreselected portion of the film which did not undergo complete melting.

In a preferred first embodiment of the technique, an irradiatedstructure includes a substrate-supported first semiconductor film, aheat-resistant film on the first semiconductor film, and a secondsemiconductor film on the heat-resistant film. In this embodiment, bothfront and back sides of the structure are irradiated with a pulse.

In a preferred second embodiment, lateral solidification is from a firstregion via a constricted second region to a third region which isintended as a device region. One-sided irradiation is used in thisembodiment, in combination with area heating through the substrate.

In a preferred third embodiment, a beam is pulsed repeatedly in formingan extended single-crystal region as a result of laterally stepping aradiation pattern for repeated melting and solidification.

Advantageously, the technique can be used in the manufacture ofhigh-speed liquid crystal display devices, wherein pixel controllersor/and driver circuitry are made in single-crystal orregular/quasi-regular polycrystalline films. Other applications includeimage sensors, static random-access memories (SRAM),silicon-on-insulator (SOI) devices, and three-dimensional integratedcircuit devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a projection irradiation systemas can be used for the first embodiment of the technique.

FIG. 2 is a schematic, greatly enlarged side view of a sample structurefor the first embodiment.

FIGS. 3A and 3B are schematic, greatly enlarged top views of TFT devicemicrostructures which can be made in semiconductor material of the firstembodiment.

FIG. 4 is a schematic representation of an irradiation system as can beused for the second embodiment of the technique.

FIG. 5 is a schematic, greatly enlarged side view of a sample structurefor the second embodiment.

FIGS. 6A-6D are schematic top views of the sample structure of FIG. 5 atsequential stages of processing.

FIG. 7 is a schematic representation of an irradiation system as can beused for the third embodiment.

FIG. 8 is a schematic, greatly enlarged side view of a sample structurefor the third embodiment.

FIGS. 9A-9F are schematic top views of a sample structure with side viewas in FIG. 8 at sequential stages in a first version of a first variantof processing.

FIGS. 10A-10F are schematic top views of a sample structure with sideview as in FIG. 8 at sequential stages in a second version of the firstvariant of processing.

FIGS. 11A-11C are schematic top views of a sample structure atsequential stages of a second variant of processing.

FIG. 12 is a schematic top view of a liquid-crystal display device inwhich TFTs are included.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Described in the following are specific, experimentally realizedexamples, as well as certain variations thereof. Explicitly orimplicitly, some variations are common to more than one of theembodiments, and further variations, within the scope of the claims,will be apparent to those skilled in the art. Included, e.g., is the useof semiconductor materials other than silicon, such as germanium,silicon-germanium, gallium arsenide or indium phosphide, for example.Included also is the use of a substrate of any suitable material, e.g.,silicon dioxide, quartz, glass or plastic, subject to considerations ofstability, inertness and heat resistance under processing conditions.And included is the use of a radiation beam other than a laser beam,e.g., an electron or ion beam.

First Embodiment

The projection irradiation system of FIG. 1 includes an excimer laser11, mirrors 12, a beam splitter 13, a variable-focus field lens 14, apatterned projection mask 15, a two-element imaging lens 16, a samplestage 17, a variable attenuator 18 and a focusing lens 19. With thissystem, simultaneous radiation pulses can be applied to the front andback sides of a sample 10 on the stage 17.

For the first embodiment of the technique, a “dual-layer” (DL) samplestructure was prepared as shown in FIG. 2, including a transparentsubstrate 20, a first amorphous silicon film 21, an SiO₂ film 22, and asecond amorphous silicon film 23. Film thicknesses were 100 nanometersfor the amorphous silicon films and 500 nanometers for the SiO₂ film.Alternative heat-resistant materials such as, e.g., silicon nitride or ahigh-temperature glass may be used for the film 22.

With pattern projection onto the second or top silicon film 23 andbroad-beam irradiation of the first or bottom silicon film 21, the firstsilicon film 21 can be regarded as a sacrificial layer which is includedfavorably to affect the thermal environment for maximized lateralcrystal growth in the top silicon film 23. The roles of these films isreversed if, alternatively, the pattern is projected through thesubstrate onto the first film. In the pattern-irradiated film, large,laterally solidified grains will be formed, making the processed filmwell-suited for TFTs, for example.

Structures in accordance with FIG. 2 were prepared by sequentiallow-pressure chemical vapor deposition (LPCVD) of a-Si, SiO₂, and againa-Si on a quartz substrate. Other suitable deposition methods, forproducing amorphous or microcrystalline deposits, includeplasma-enhanced chemical vapor deposition (PECVD), evaporation orsputtering, for example.

Samples were placed onto the stage 17 of the projection irradiationsystem of FIG. 1. The mask 15 had a pattern of simple stripes 50micrometers wide, with various separation distances from 10 to 100micrometers.

The mask pattern was projected onto the samples with different reductionfactors in the range from 3 to 6. The back-side energy density wascontrolled by the variable attenuator 18. Samples were irradiated atroom temperature with a 30-nanosecond XeCl excimer laser pulse having awavelength of 308 nanometers, quartz being transparent at thiswavelength. Such a laser is commercially available under the designationLambdaPhysik Compex 301. For a glass substrate, a longer wavelengthwould have been required, e.g., 348 nanometers.

Irradiation was with fixed front-side energy density and with variousback-side energy densities. Estimated front-side energy density wasapproximately 1.0 J/cm² at the sample plane. The back-side energydensities were in the range from 170 to 680 mJ/cm².

For examination subsequent to irradiation, the films were thoroughlydefect-etched using Secco etchant and examined using scanning electronmicroscopy (SEM). The largest, most uniform grains were obtained at aback-side energy density of 510 mJ/cm². These grains grew laterally fromthe two sides of stripe regions, forming two rows of grains with awell-defined grain boundary at the center line of the stripe.

Even if the resulting individual crystals may not be large enough toaccommodate the entire active-channel region of a TFT, they form aregular or quasi-regular polycrystalline structure which can serve asactive-channel region of a TFT, e.g., as illustrated in FIG. 3A or FIG.3B. Shown are a source electrode 31, a drain electrode 32, a gateelectrode 33 and an active-channel region 34. In FIG. 3A, theactive-channel region includes both rows of grains produced as describedabove. With grains sufficiently large as in FIG. 3B, the active-channelregion can be formed by a single row of grains.

In processing according to the first embodiment, the role of thesacrificial bottom film 21 may be understood as being that of a heatsusceptor which stores energy when heated by the beam, the greatestbenefit being obtained when this film melts. The stored heat is releasedduring solidification. This decreases the degree to which the top film23 loses heat by conduction. Accordingly, for maximum benefit, care iscalled for in proper dimensioning of the irradiated structure. If theSiO₂ film 22 is too thin, the thermal evolution of the silicon films 21and 23 will tend to track together, without significant benefit from theinclusion of the film 21. On the other hand, if the film 22 is too thickwith respect to the thermal diffusion length of the physical process,the film 21 will have insufficient influence on the transformation inthe top film 23. As to the bottom film 21, its thickness should bechosen for this film to have sufficient thermal mass. But the thickerthe film 21, the more energy will be required for its melting.

As alternatives to projection of a pattern onto the silicon layer 23, adesired pattern may be defined there by a proximity mask, a contactmask, or a deposited mask layer which is patternedphoto-lithographically, for example.

In one variant of masking, a mask layer may serve to reduce heating inthe area beneath the mask, e.g., by absorbing or reflecting incidentradiation. Alternatively, with a suitable mask material of suitablethickness, a complementary, anti-reflection effect can be realized tocouple additional energy into the semiconductor film beneath the maskmaterial. For example, an SiO₂ film can be used to this effect on asilicon film. This variant is advantageous further in that the masklayer can serve as a restraint on the molten semiconductor material,thus preventing the molten semiconductor layer from agglomerating ordeforming under surface tension.

Second Embodiment

The irradiation system of FIG. 4 includes an excimer laser 41, a prismdeflector 42, a focusing lens 43, a vacuum chamber 44 and a hot stage 45on which a sample 40 is disposed.

For the second embodiment of the technique and using the irradiationsystem of FIG. 4, the sample structure of FIG. 5 includes a substrate50, a thermal oxide film 51, a first patterned amorphous silicon film52, an SiO₂ film 53, a second patterned silicon film 54, and a furtherdeposited SiO₂ film 55. Typical thicknesses are 100 nanometers for thethermal oxide film 51, 100 nanometers for the a-Si film 52, 210nanometers for the SiO₂ film 53, 120 nanometers for the a-Si film 54,and 170 nanometers for the SiO₂ film 55.

Such a sample structure was prepared by depositing the amorphous siliconfilm 52 by low-pressure chemical vapor deposition (LPCVD) onto thethermal oxide film 51 on a silicon wafer 50. The silicon film 52 wascoated with a photoresist which was then exposed in a stepper anddeveloped, and the silicon film 52 was reactively ion-etched in SF₆/O₂plasma for patterning. The resulting pattern of a “first-level island”of the silicon film 52 is shown in FIG. 6A as viewed from the top. Thepattern consists of three parts: a square “main-island” region 523 whichis intended for eventual device use, a rectangular “tail” region 521,and a narrow “bottleneck” region 522 connecting the tail region 521 withthe main-island region 523. Dimensions were chosen as follows: 20 by 10micrometers for the tail region 521, 5 by 3 micrometers for thebottleneck region 522, and different dimensions in the range from 10 by10 to 50 by 50 micrometers for the main-island region 521.

The first-level islands were encapsulated with the SiO₂ film 53 byplasma-enhanced chemical-vapor deposition (PECVD), and amorphous siliconwas deposited on top. Photolithographic processing was used again, forpatterning the amorphous silicon film as a “second-level island” 54dimensioned 5 by 5 micrometers. The second-level island 54 is positioneddirectly above the tail region 521 to serve as a beam blocker duringirradiation. Last, the entire structure was encapsulated with PECVDSiO₂.

For processing, a sample was placed on a resistively heated graphite hotstage inside a vacuum chamber at a pressure of 10⁻⁵ torr.Vacuum-processing can be dispensed with if a suitable alternative heateris available. Heating was to a substrate temperature of 1000 to 1200°C., which required a ramp-up time interval of about three minutes.Before irradiation, the sample was held at the final substratetemperature for approximately two minutes. The sample temperature wasmonitored occasionally by a directly attached thermocouple andcontinuously by a digital infrared thermometer. The sample wasirradiated with a single excimer-laser pulse at energy densities thatwere sufficiently high to completely melt all of the first-level islandexcept for the beam-blocked area within the tail region.

For analysis of the microstructure, the irradiated samples wereSecco-etched. For samples irradiated at a substrate temperature of 1150°C., optical Nomarski micrographs of the Secco-etched samples showedcomplete conversion of islands 20 by 20, 40 by 40 and 50 by 50micrometers into single-crystal islands (SCI). Defect patterns in theetched samples suggest that the main-island zones contain low-anglesub-boundaries similar to those observed in zone meltingrecrystallization (ZMR), as well as planar defects which have beenidentified in SLG studies. At a lower substrate temperature, such as at1100° C., only the smaller, 20-by-20 micrometer islands were convertedinto single-crystal islands free of high-angle grain boundaries. And atstill-lower substrate temperatures of 1050° C. and 1000° C., high-anglegrain boundaries appeared even in the 20 by 20 micrometer islands.

The solidification sequence in this second embodiment may be understoodwith reference to FIGS. 6B-6D as follows: Upon irradiation, thesecond-level square 54 blocks most of the beam energy incident on thearea, which prevents complete melting in the beam-blocked area of thetail region 521. The rest of the exposed first level regions meltscompletely as illustrated by FIG. 6B. As the film is conductively cooledthrough the substrate, the liquid-solid interface at the beam-blockedregion undercools, and silicon grains 61 start to grow radially outwardfrom the beam-blocked region. Within the tail region 521, many of thegrains 61 are quickly occluded, and only one or a few favorably locatedgrains grow toward the bottleneck 522. The bottleneck 522 is configuredsuch that just one of these grains expands through the bottleneck 522into the main-island region 523. If the substrate temperature is highenough and the main island 523 is small enough to prevent nucleation inthe super-cooled liquid, lateral growth of the one grain that grewthrough the bottleneck 522 converts the entire main island 523 into asingle-crystal region.

Thus, successful conversion of the main-island region 523 intosingle-crystal form requires a suitable combination of substratetemperature and island size. The molten silicon must be sustained at atemperature which is sufficiently high for the characteristic time ofnucleation for a specific volume to be much longer than thecharacteristic time required for the complete conversion by lateralsolidification. Since the characteristic conversion time depends mainlyon the distance to be converted, i.e., the lateral dimension of the mainisland, the island size must be related to the substrate temperaturesuch that the characteristic conversion time is commensurate with theaverage lateral growth distance that can be achieved before anynucleation is triggered within the liquid. As compared with zone-meltingrecrystallization, the present technique allows the recrystallization ofvery thin films, e.g., having a thickness of 100 nanometers or less.

Instead of by beam blocking, a seed region can be defined bycomplementary masking with an anti-reflection film, as described abovefor the first embodiment. Alternatively further, a seed region can bedefined by projection.

Third Embodiment

The projection irradiation system of FIG. 7 includes an excimer laser71, mirrors 72, a variable-focus field lens 74, a patterned mask 75, atwo-element imaging lens 76, a sample stage 77, and a variableattenuator 78. A sample 70 is disposed on the sample stage 77. Thissystem can be used to produce a shaped beam for stepped growth of asingle-crystal silicon region in a sequential lateral solidification(SLS) process. Alternatively, a proximity mask or even a contact maskmay be used for beam shaping.

The sample structure of FIG. 8 has a substrate 80, a thermal oxide film81, and an amorphous silicon film 82.

In the following, the third embodiment of the technique is describedwith reference to FIGS. 9A-9F and 10A-10F showing two versions of afirst variant, and FIGS. 11A-11B showing a second variant.

Starting with the amorphous silicon film 82, which in this exemplaryembodiment is patterned as a rectangle (FIG. 9A), a region 91, boundedby two broken lines, of the silicon film 82 is irradiated with a pulse,to completely melt the silicon in that region (FIG. 9B), and thenresolidify the molten silicon (FIG. 9C) in the region 91. Here, theregion 91 is in the shape of a stripe, and irradiation of the region 91may be by masked projection or by use of a proximity mask. Uponresolidification of the molten silicon in the region 91, two rows ofgrains grow explosively from the broken line boundaries of the region 91towards the center of the region 91. Growth of the two rows of grains isover the characteristic lateral growth to a final distance 92. In anyremainder of region 91, a fine grained polycrystalline region 93 isformed. Preferably, the width of the stripe is chosen such that, uponresolidification, the two rows of grains approach each other withoutconverging. Greater width, which is not precluded, does not contributeto the efficacy of processing. Lesser width tends to be undesirablesince the subsequent step may have to be reduced in length, and thesemiconductor surface may become irregular where grains growing fromopposite directions come together during the solidification process. Anoxide cap may be formed over the silicon film to retard agglomerationand constrain the surface of the silicon film to be smooth.

A next region to be irradiated is defined by shifting (stepping) thesample with respect to the masked projection or proximity mask in thedirection of crystal growth. The shifted (stepped) region 94 is boundedby two broken lines in FIG. 9D. The distance of the shift is such thatthe next region to be irradiated 92 overlaps the previously irradiatedregion 91 so as to completely melt one row of crystals while partiallymelting the other row of crystals, as shown in FIG. 9E. Uponresolidification, the partially melted row of crystals will becomelonger, as shown in FIG. 9F. In this fashion, by repeatedly shifting theirradiated portion, single crystalline grains of any desired length maybe grown.

If the pattern of the irradiated region is not a simple stripe, but isin the shape of a chevron 101, as defined by the broken lines in FIG.10A, the same sequence of shifting the irradiated region shown in FIGS.10B-10F will result in the enlargement of one grain growing from theapex of the trailing edge of the shifting (stepping) chevron pattern. Inthis manner, a single-crystal region can be grown with increasing widthand length.

A large area single-crystal region can also be grown by applyingsequentially shifted (stepped) irradiation regions to a patternedamorphous silicon film, such as that illustrated in FIG. 11A, having atail region 111, a narrow bottleneck region 112 and a main island region113. The cross-section of regions 111, 112 and 113 in FIGS. 11A-11C issimilar to that shown in FIG. 5, except that the radiation blockingamorphous silicon region 54 and the second silicon dioxide layer 55 areabsent. The region of irradiation defined by masked projection or aproximity mask is illustrated by the regions bounded by broken lines inFIGS. 11A-11C, which also show the sequential lateral shifting(stepping) of the irradiated region to obtain the growth of a singlegrain from the tail region 111 through the bottleneck region 112 toproduce a single crystal island region 113.

Sequential lateral melting and resolidification in the examples of FIGS.9A-9F, 10A-10F and 11A-11C were carried out on amorphous silicon filmswhich had been deposited by chemical vapor deposition (CVD) on a silicondioxide coated quartz substrate, with film thicknesses from 100 to 240nanometers. The production of single-crystal stripes was confirmed inoptical and scanning electron microscopic examination of defect-etchedsamples.

Optionally, the substrate may be heated, e.g., to reduce the beam energyrequired for melting or to lengthen the lateral growth distance perstep. Such benefits may be realized also by two-sided irradiation of asample on a stage as shown in FIG. 1.

FURTHER PROCESSING AND APPLICATIONS

With a semiconductor film processed by the present technique, integratedsemiconductor devices can be manufactured by well-established furthertechniques such as pattern definition, etching, dopant implantation,deposition of insulating layers, contact formation, and interconnectionwith patterned metal layers, for example. In preferred thin-filmsemiconductor transistors, at least the active-channel region has asingle-crystal, regular or at least quasi-regular microstructure, e.g.,as illustrated by FIGS. 3A and 3B.

Of particular interest is the inclusion of such TFTs in liquid-crystaldisplay devices as schematically shown in FIG. 12. Such a deviceincludes a substrate 120 of which at least a display window portion 121is transparent. The display window portion 121 includes a regular arrayof pixels 122, each including a TFT pixel controller. Each pixelcontroller can be individually addressed by drivers 123. Preferably,pixel controllers or/and driver circuitry are implemented insemiconductor material processed in accordance with the technique of thepresent invention.

Other applications include image sensors, static random-access memories(SRAM), silicon-on-insulator (SOI) devices, and three-dimensionalintegrated circuit devices.

What is claimed is:
 1. A method for making a polycrystalline region as alaterally extending portion of a supported film of semiconductormaterial, comprising: simultaneously irradiating, with pulsed radiationwhich induces heat in the semiconductor material, front and back sidesof a structure comprising a radiation-permeable substrate in back, afirst semiconductor film on the substrate, a heat-resistant film on thefirst semiconductor film, and a second semiconductor film on theheat-resistant film, so as to melt all semiconductor material in alaterally extending region of the one of the semiconductor films whichincludes the portion, so that, after the simultaneous irradiation, apolycrystalline microstructure is formed in the region by lateralsolidification from a boundary of the region.
 2. The method of claim 1,wherein the region is delimited by parallel edges.
 3. The method ofclaim 2, wherein the parallel edges are spaced apart by a distance forwhich simultaneous lateral solidification from the edges results incomplete crystallization of the region.
 4. The method of claim 1,wherein the semiconductor material comprises silicon.
 5. The method ofclaim 1, wherein the heat-resistant layer consists essentially of SiO₂.6. The method of claim 1, wherein the substrate is a glass substrate. 7.The method of claim 1, wherein the substrate is a quartz substrate. 8.The method of claim 1, wherein the laterally extending portion is in thefirst semiconductor film.
 9. The method of claim 1, wherein thelaterally extending portion is in the second semiconductor film.
 10. Themethod of claim 1, wherein the region has a shape defined by a maskpattern.
 11. The method of claim 10, wherein the mask pattern isprojected.
 12. The method of claim 10, wherein the mask pattern isdefined by a proximity mask.
 13. The method of claim 10, wherein themask pattern is defined by a contact mask.
 14. The method of claim 1,wherein the radiation comprises laser radiation.
 15. The method of claim1, wherein the laterally extending region is encapsulated.
 16. On asupporting substrate, a semiconductor film processed by the method ofclaim
 1. 17. On a supporting substrate, a plurality of semiconductordevices in a semiconductor film processed by the method of claim
 1. 18.On a supporting substrate, an integrated circuit comprising a pluralityof thin-film transistors in which at least the active-channel region isprocessed by the method of claim
 1. 19. A liquid-crystal display devicecomprising a plurality of pixel-controller thin-film transistors inwhich at least the active-channel region is processed by the method ofclaim
 1. 20. A liquid-crystal display device comprising a pixel-driverintegrated circuit which comprises a plurality of thin-film transistorsin which at least the active-channel region is processed by the methodof claim
 1. 21. A method for making a laterally extending crystallineregion in a film of semiconductor material on a substrate, comprising:irradiating, with pulsed radiation which induces heat in thesemiconductor material, a portion of the semiconductor film so as toentirely melt the semiconductor material in the portion, and permittingthe molten semiconductor material in the portion to solidify; wherein:the portion is configured so as to include a first sub-portion, a secondsub-portion which is contiguous to the first sub-portion, and a thirdsub-portion which is contiguous to the second sub-portion, the firstsub-portion being configured for nucleation of semiconductor crystals atits boundary, the second sub-portion being configured such that just oneof the nucleated crystals grows from the first sub-portion through thesecond sub-portion into the third sub-portion, and the third sub-portionbeing configured such that the one crystal occupies the thirdsub-portion in its entirety.
 22. The method of claim 21, wherein thefirst sub-portion is configured with an island portion for nucleation ofsemiconductor crystals.
 23. The method of claim 22, wherein the islandportion has a shape defined by a mask pattern.
 24. The method of claim23, wherein the mask pattern is projected.
 25. The method of claim 23,wherein the mask pattern is defined by a proximity mask.
 26. The methodof claim 23, wherein the mask pattern is defined by a contact mask. 27.The method of claim 21, wherein the configuration of the secondsub-portion precludes a straight-line path between the first sub-portionand the third sub-portion.
 28. The method of claim 21, wherein thesemiconductor material comprises silicon.
 29. The method of claim 21,wherein the substrate is heated.
 30. The method of claim 21, wherein thesubstrate is a glass substrate.
 31. The method of claim 21, wherein thesubstrate is a quartz substrate.
 32. The method of claim 21, wherein thepulsed radiation is applied to front and back of the semiconductor film.33. The method of claim 21, wherein the semiconductor film has athickness not exceeding 100 nanometers.
 34. The method of claim 21,wherein the radiation comprises laser radiation.
 35. The method of claim21, wherein the portion is encapsulated.
 36. On a supporting substrate,a semiconductor film processed by the method of claim
 21. 37. On asupporting substrate, a plurality of semiconductor devices in asemiconductor film processed by the method of claim
 21. 38. On asupporting substrate, an integrated circuit comprising a plurality ofthin-film transistors in which at least the active-channel region isprocessed by the method of claim
 21. 39. A liquid-crystal display devicecomprising a plurality of pixel-controller thin-film transistors inwhich at least the active-channel region is processed by the method ofclaim
 21. 40. A liquid-crystal display device comprising a pixel-driverintegrated circuit which comprises a plurality of thin-film transistorsin which at least the active-channel region is processed by the methodof claim
 21. 41. A method for making a laterally extending crystallineregion in a film of semiconductor material on a substrate having atleast a surface region consisting of a material which is different fromthe semiconductor material of the film and which is inert with respectto crystal growth in the film of semiconductor material, comprising: (a)providing a film of semiconductor material to be crystallized directlyon the at least a surface region of the substrate; (b) irradiating, withpulsed radiation which induces heat in the semiconductor material, afirst portion of the film so as to melt the semiconductor material inthe first portion throughout its thickness; (c) permitting thesemiconductor material in the first portion to laterally solidify,thereby forming at least one semiconductor crystal at a boundary of thefirst portion, the first portion then being a previous portion forfurther processing; (d) irradiating a further portion of thesemiconductor material, which is stepped from the previous portion in astepping direction and which overlaps the at least one semiconductorcrystal in part, so as to melt the semiconductor material in the furtherportion throughout its thickness; (e) permitting the moltensemiconductor material in the further portion to laterally solidify,thereby enlarging the at least one semiconductor crystal by growth inthe stepping direction; (f) repeating steps (d) and (e) in combinationwith the further portion of each step becoming the previous portion ofthe next step, until the laterally extending crystalline region isformed.
 42. The method of claim 41, wherein the irradiated portions arestripes.
 43. The method of claim 42, wherein the stripes have a widthbetween edges such that simultaneous lateral solidification from theedges does not result in complete crystallization of the stripes. 44.The method of claim 41, wherein the semiconductor material comprisessilicon.
 45. The method of claim 41, wherein the irradiated portions arechevrons.
 46. The method of claim 41, wherein the substrate is a glasssubstrate.
 47. The method of claim 41, wherein the substrate is a quartzsubstrate.
 48. The method of claim 41, wherein the laterally extendingcrystalline region is defined by patterning the film of semiconductormaterial.
 49. The method of claim 48, wherein the pattern of the filmcomprises a tail portion, a bottleneck portion which is contiguous tothe tail portion, and a main-island portion which is contiguous to thebottleneck portion, and wherein the first portion of the film irradiatedwith the pulse radiation is in the tail portion of the film, and thefurther irradiated portions are in a stepping direction that firstpasses through the tail portion and then passes through the bottleneckportion and finally passes through the main-island portion.
 50. Themethod of claim 41, wherein the irradiated portions are defined by amask pattern.
 51. The method of claim 50, wherein the mask pattern isprojected.
 52. The method of claim 50, wherein the mask pattern isdefined by a proximity mask.
 53. The method of claim 50, wherein themask pattern is defined by a contact mask.
 54. The method of claim 41,wherein the radiation comprises laser radiation.
 55. The method of claim41, wherein the laterally extending region is encapsulated.
 56. On asupporting substrate, a semiconductor film processed by the method ofclaim
 41. 57. On a supporting substrate, a plurality of semiconductordevices in a semiconductor film processed by the method of claim
 41. 58.On a supporting substrate, an integrated circuit comprising a pluralityof thin-film transistors in which at least the active-channel region isprocessed by the method of claim
 41. 59. A liquid-crystal display devicecomprising a plurality of pixel-controller thin-film transistors inwhich at least the active-channel region is processed by the method ofclaim
 41. 60. A liquid-crystal display device comprising a pixel-driverintegrated circuit which comprises a plurality of thin-film transistorsin which at least the active-channel region is processed by the methodof claim
 41. 61. An apparatus for making a laterally extendingcrystalline region in a film of semiconductor material on the substratehaving at least a surface region consisting of a material which isdifferent from the semiconductor material of the film and which is inertwith respect to crystal growth in the film of semiconductor material,comprising: (a) a pulsed laser for providing laser beam pulses; (b) abeam mask through which the laser beam pulses pass for defining maskedlaser beam pulses each having a intensity pattern for irradiating thefilm of semiconductor material; (c) a sample translation stage forholding the substrate having the film of semiconductor material while atleast a portion of the film of semiconductor material is beingirradiated by a masked laser beam pulse, and for translating thesubstrate having the film of semiconductor material in a lateraldirection with respect to the masked beam pulses; (d) a first opticalpath traversed by the laser beam pulses from the laser to the beam mask;and (e) a variable attenuator for attenuating the intensities of themasked laser beam pulses, wherein when the sample translation stage isin a first position, a first portion of the semiconductor film isirradiated by a masked radiation beam pulse so as to melt thesemiconductor material in the first portion throughout its thickness,the molten semiconductor material in the first portion being permittedto laterally solidify so as to form at least one semiconductor crystalat the boundary of the first portion, which then becomes a previousportion for further processing, wherein the sample translation stage ismoved in the lateral direction to a next position at which a nextportion of the film of semiconductor material which overlaps the atleast one semiconductor crystal in part is irradiated by another maskedradiation beam pulse so a to melt the semiconductor material in the nextportion throughout its thickness, the molten semiconductor material inthe next portion being permitted to laterally solidify so as to enlargethe at least one semiconductor crystal by growth in the lateraldirection, and wherein the sample translation stage is repeatedly movedin the lateral direction to a further position at which a furtherportion of the film of semiconductor material is irradiated by a furthermasked radiation beam pulse after the previous portion has beenpermitted to laterally solidify, each further portion overlapping the atleast one semiconductor crystal of the previous portion in part so as toenlarge the at least one semiconductor crystal by growth in the lateraldirection until a desired crystalline region is formed.
 62. An apparatusfor making a laterally extending crystalline region in the film ofsemiconductor material on the substrate having at least a surface regionconsisting of a material which is different from the semiconductormaterial of the film and which is inert with respect to crystal grow inthe film of semiconductor material, comprising: (a) a pulsed radiationbeam source for providing radiation beam pulses; (b) a beam mask throughwhich the radiation beam pulses pass for defining masked radiation beampulses each having an intensity pattern in the shape of at least onechevron for irradiating the film of semiconductor material; and (c) asample translation stage for holding the substrate having the film ofsemiconductor material while at least a portion of the film ofsemiconductor material is being irradiated by a masked radiation beampulse, and for translating the substrate having the film ofsemiconductor material in a lateral direction with respect to the maskedradiation beam pulses, wherein when the sample translation stage is in afirst position, a first portion of the film is irradiated by a maskedradiation beam pulse so as to melt the semiconductor material in thefirst portion throughout its thickness, the molten semiconductormaterial in the first portion being permitted to laterally solidify soas to form at least one semiconductor crystal at the boundary of thefirst portion, which then becomes the previous portion for furtherprocessing, wherein the sample translation stage is moved in the lateraldirection to a next position at which a next portion of the film ofsemiconductor material which overlaps the at least one semiconductorcrystal in part is irradiated by another masked radiation beam pulse soas to melt the semiconductor material in the next portion throughout itsthickness, the molten semiconductor material in the next portion beingpermitted to laterally solidify so as to enlarge the at least onesemiconductor crystal by growth in the lateral direction, and whereinthe sample translation stage is repeatedly moved in the lateraldirection to a further position at which a further portion of the filmof semiconductor material is irradiated by a further masked radiationbeam pulse after the previous portion has been permitted to laterallysolidify, each further portion overlapping the at least onesemiconductor crystal of the previous portion in part so as to enlargethe at least one semiconductor crystal by growth in the lateraldirection until the desires crystalline region is formed.